EP3153920B1 - In-plane switching liquid crystal display comprising compensation film for angular field of view using positive biaxial retardation film - Google Patents
In-plane switching liquid crystal display comprising compensation film for angular field of view using positive biaxial retardation film Download PDFInfo
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- EP3153920B1 EP3153920B1 EP16195465.6A EP16195465A EP3153920B1 EP 3153920 B1 EP3153920 B1 EP 3153920B1 EP 16195465 A EP16195465 A EP 16195465A EP 3153920 B1 EP3153920 B1 EP 3153920B1
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- Prior art keywords
- liquid crystal
- polarizer plate
- film
- retardation film
- positive biaxial
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- 239000004973 liquid crystal related substance Substances 0.000 title claims description 68
- 238000010521 absorption reaction Methods 0.000 claims description 34
- 230000001681 protective effect Effects 0.000 claims description 33
- 230000003287 optical effect Effects 0.000 claims description 25
- 210000002858 crystal cell Anatomy 0.000 claims description 21
- 239000006185 dispersion Substances 0.000 claims description 6
- 239000010408 film Substances 0.000 description 140
- 229920000089 Cyclic olefin copolymer Polymers 0.000 description 12
- 238000004088 simulation Methods 0.000 description 10
- 239000000758 substrate Substances 0.000 description 6
- 239000011159 matrix material Substances 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 3
- 229920002678 cellulose Polymers 0.000 description 3
- 239000001913 cellulose Substances 0.000 description 3
- 239000011521 glass Substances 0.000 description 3
- ILJSQTXMGCGYMG-UHFFFAOYSA-N triacetic acid Chemical compound CC(=O)CC(=O)CC(O)=O ILJSQTXMGCGYMG-UHFFFAOYSA-N 0.000 description 3
- 210000004027 cell Anatomy 0.000 description 2
- 239000004417 polycarbonate Substances 0.000 description 2
- 238000002834 transmittance Methods 0.000 description 2
- 239000004988 Nematic liquid crystal Substances 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000012788 optical film Substances 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
- 239000002861 polymer material Substances 0.000 description 1
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/13363—Birefringent elements, e.g. for optical compensation
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1343—Electrodes
- G02F1/134309—Electrodes characterised by their geometrical arrangement
- G02F1/134363—Electrodes characterised by their geometrical arrangement for applying an electric field parallel to the substrate, i.e. in-plane switching [IPS]
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/13363—Birefringent elements, e.g. for optical compensation
- G02F1/133634—Birefringent elements, e.g. for optical compensation the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
- G02F2201/12—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 electrode
- G02F2201/124—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 electrode interdigital
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2202/00—Materials and properties
- G02F2202/40—Materials having a particular birefringence, retardation
Definitions
- the present invention relates to a liquid crystal display (LCD), and more particularly to an in-plane switching liquid crystal display (IPS-LCD) including a compensation film, which uses a positive biaxial retardation film while adjusting an optical axis direction and a retardation value of the positive biaxial retardation film in order to improve a viewing angle characteristic of the in-plane switching liquid crystal display having a liquid crystal cell filled with liquid crystal of positive dielectric anisotropy ( ⁇ >0) or negative dielectric anisotropy ( ⁇ 0).
- IPS-LCD in-plane switching liquid crystal display
- Electrodes of an IPS-LCD are aligned in such a manner that an electric field is applied in parallel to a liquid crystal plane of the IPS-LCD.
- Surfaces of a liquid crystal layer adjacent to two substrates have pretilt angles in a range of 0° to 5° as disclosed in U.S. Patent No. 6,078,375 .
- An IPS panel liquid crystal cell
- the active matrix drive electrode provides IPS (In-Plain Switching), S-IPS (Super-In-Plain Switching) and FFS (Fringe Field Switching) modes to a liquid crystal layer formed between two glass substrates.
- IPS In-Plain Switching
- S-IPS Super-In-Plain Switching
- FFS Frringe Field Switching
- the IPS-LCD is disclosed in U.S. Patent No. 3,807,831 .
- the IPS-LCD disclosed in U.S. Patent No. 3,807,831 does not use a compensation film. Accordingly, the IPS-LCD represents a low contrast ratio at a predetermined inclination angle due to a relatively great amount of light leakage.
- U.S. Patent No. 5,189,538 discloses an LCD including two kinds of retardation films, such as a +A-plate and a positive biaxial retardation film, but it does not disclose information or technologies about the IPS-LCD.
- U.S. Patent No. 5,440,413 discloses a TN-LCD having two positive biaxial retardation films in order to improve the contrast characteristic and color characteristic of the TN-LCD at a predetermined inclination angle.
- KR 2003 0079705 A discloses an optical film with a liquid crystal cell, a first and a second polarizer plate and a biaxial retardation film arranged between the liquid crystal cell and the second polarizer plate.
- the biaxial retardation film has a N z value of from 0.4 to 0.6 and an in-plane retardation value Re in of from 200 to 350 nm.
- Protective films can be applied on the polarizing plates, wherein the protective films have an in-plane retardation value Re in of 20 nm or less and a thickness retardation value R th of 30 nm or less.
- a main object of using the biaxial retardation film is to improve a contrast characteristic of the IPS-LCD at an inclination angle in all azimuthal angles, especially 45°, 135°, 225° and 315°.
- the contrast characteristic of the IPS-LCD can be improved at the above azimuthal angles, the IPS-LCD in a black state represents a great amount of light leakage at other azimuthal angles. For this reason, a contrast ratio of the IPS-LCD is relatively reduced at other azimuthal angles. Therefore, the above IPS-LCD has a disadvantage in that the IPS-LCD represents a relatively low contrast ratio at specific azimuthal angles due to relatively great light leakage in the black state.
- Another object of the present invention is to provide an IPS-LCD representing low transmittance in a black state at all inclination angles in all azimuthal angles.
- the present invention accomplishes the above object by using a positive biaxial retardation film while adjusting an optical axis direction and the retardation value of the positive biaxial retardation film.
- an in-plane switching liquid crystal display comprising: a first polarizer plate; a second polarizer plate; and a liquid crystal cell, which is horizontally aligned between two glass substrates and filled with liquid crystal of positive dielectric anisotropy ( ⁇ >0) or negative dielectric anisotropy ( ⁇ 0), an optical axis of the liquid crystal filled in the liquid crystal cell being aligned in-plane in parallel to the first and second polarizer plates, wherein an absorption axis of the first polarizer plate is perpendicular to an absorption axis of the second polarizer plate, the optical axis of the liquid crystal filled in the liquid crystal cell is parallel to the absorption axis of the first polarizer plate, a positive biaxial retardation film is aligned between the liquid crystal cell and the polarizer plate in order to compensate for a viewing angle, and an optical axis direction and a retardation value of the positive biaxial retardation film are adjusted according to an alignment order of positive
- the present invention is characterized by using at least one positive biaxial retardation film in which an optical axis direction and a retardation value of the positive biaxial retardation film are adjusted according to upper and lower polarizer plates and an alignment order of the positive biaxial retardation films.
- a contrast ratio is an index representing a degree of definition for an image, and a high contrast ratio allows a high definition image.
- the contrast characteristic of the IPS-LCD is most deteriorated at an inclination angle of 70°.
- the IPS-LCD represents an improved contrast characteristic at the inclination angle of 70°, it means that the contrast characteristic of the IPS-LCD is improved at all viewing angles. Accordingly, comparison of improvement for viewing angle characteristics of IPS-LCDs is preferably carried out with the inclination angle of 70°.
- a minimum contrast ratio at the inclination angle of 70° is equal to or less than 10:1.
- the IPS-LCD of the present invention uses the positive biaxial retardation film while adjusting the optical axis and the retardation value thereof, so the IPS-LCD of the present invention may represent a minimum contrast ratio above 20:1.
- the IPS-LCD of the present invention represents the minimum contrast ratio above 20:1 at the inclination angle of 70°.
- FIG. 1 is a view illustrating a basic structure of an IPS-LCD.
- the IPS-LCD includes a first polarizer plate 1, a second polarizer plate 2 and a liquid crystal cell 3.
- An absorption axis 4 of the first polarizer plate 1 is aligned in perpendicular to the an absorption axis 5 of the second polarizer plate 2 and the absorption axis 4 of the first polarizer plate 1 is parallel to an optical axis 6 of the liquid crystal cell 3.
- FIG. 2 two absorption axes 4 and 5 of two polarizer plates and one optical axis 6 of one liquid crystal cell are shown.
- the liquid crystal display using a compensation film includes the first polarizer plate 1, the liquid crystal cell 3, which is horizontally aligned between two glass substrates and filled with liquid crystal of positive dielectric anisotropy ( ⁇ >0) or negative dielectric anisotropy ( ⁇ 0), and the second polarizer plate 2.
- the optical axis 6 of the liquid crystal filled in the liquid crystal cell 3 is aligned in-plane in parallel to the polarizer plates.
- the absorption axis 4 of the first polarizer plate 1 is aligned in perpendicular to the absorption axis 5 of the second polarizer plate 2 and the absorption axis 4 of the first polarizer plate 1 is parallel to the optical axis 6 of the liquid crystal filled in the liquid crystal cell 3.
- one of the first and second substrates includes an active matrix drive electrode having a pair of electrodes, which is formed on a surface of the substrate adjacent to a liquid crystal layer.
- the liquid crystal layer of the IPS panel according to the present invention has a retardation value in a range of 200nm to 400nm at a wavelength of 550nm.
- the light linearly polarized at 90° after passing through the first polarizer plate must be linearly polarized into 0° after it has passed through the liquid crystal layer.
- the retardation value of the liquid crystal layer of the IPS-LCD must be a half wavelength of 589nm (a monochromatic light representing a highest brightness which a person can feel). Therefore, in order to allow the light to produce a white color, the retardation value of the liquid crystal layer of the IPS-LCD can be adjusted to be somewhat shorter or longer than the half wavelength of 589nm. Therefore, the retardation value is preferably in the range around 295nm corresponding to the half wavelength of 589nm.
- the LCD of the present invention may align the liquid crystal in multi-directions, or the liquid crystal may be divided into multi-regions by voltage applied thereto.
- the LCDs can be classified into IPS (In-Plain Switching) LCDs, Super-IPS (Super-In-Plain Switching) LCDs and FFS (Fringe Field Switching) LCDs according to modes of the active matrix drive electrode including a pair of electrodes.
- the IPS-LCD may include the Super-IPS LCD, the FFS LCD, and a reverse TN IPS LCD.
- FIG. 3 illustrates a refractive index of a retardation film used for compensating for a viewing angle of the IPS-LCD.
- a refractive index in an x-axis direction is n x (8)
- a refractive index in a y-axis direction is n y (9)
- a refractive index in a z-axis direction is n z (10).
- the characteristic of the retardation film depends on the refractive index.
- a biaxial retardation film represents mutually different refractive indexes in x-axis, y-axis and z-axis directions.
- the biaxial retardation film is defined as follows: n x ⁇ n y ⁇ n z
- a negative biaxial retardation film is defined as follows: n x ⁇ n y > n z
- a positive biaxial retardation film is defined as follows: n x ⁇ n y ⁇ n z
- the positive biaxial retardation film satisfying Equation 3 represents mutually different refractive indexes in x-axis, y-axis and z-axis directions, so it has an in-plane retardation value and a thickness retardation value.
- the positive biaxial retardation film signifies a film having the positive in-plane retardation value and the positive thickness retardation value.
- the wavelength dispersion characteristic of the positive biaxial retardation film includes normal wavelength dispersion, flat wavelength dispersion, and reverse wavelength dispersion.
- the unlimited example of the positive biaxial retardation film includes an UV curable liquid crystal film using a nematic liquid crystal and a biaxially oriented PC (polycarbonate).
- the direction of the optical axis of the retardation film is determined according to an alignment order of the retardation film.
- an in-plane switching liquid crystal display including a positive biaxial retardation film 11 aligned between an IPS panel 3 and a second polarizer plate 2, in which an optical axis 12 of the positive biaxial retardation film 11 is perpendicular to an absorption axis 5 of the second polarizer plate 2, with an in-plane retardation value of the positive biaxial retardation film 11 equal to or less than 190nm at a wavelength of 550nm.
- the optical axis of the retardation film relates to light leakage generated from two polarizer plates with the absorption axes thereof aligned perpendicularly to each other. That is, in order to minimize the light leakage of the polarizer plates, the in-plane optical axis of the positive biaxial retardation film must be aligned perpendicularly to the absorption axis of the polarizer plate adjacent to the positive biaxial retardation film.
- the light radiated from a backlight unit is linearly polarized after passing through the first polarizer plate, and a rotational angle of the linearly polarized light must be increased according to the inclination angle.
- the in-plane optical axis of the positive biaxial retardation film In order to rotate the linearly polarized light, the in-plane optical axis of the positive biaxial retardation film must be aligned in perpendicular to the absorption axis of the adjacent polarizer plate.
- the in-plane retardation value of the positive biaxial retardation film is preferably set equal to or less than 190nm.
- the in-plane retardation value of the positive biaxial retardation film may vary according to the thickness retardation value of the positive biaxial retardation film. In order to properly compensate for the viewing angle, it is preferred to reduce the in-plane retardation value as the total thickness retardation value of the retardation film increases.
- FIGS. 4a and 4b The first embodiment of the present invention is illustrated in FIGS. 4a and 4b , and the structures of the IPS-LCDs shown in FIGS. 4a and 4b are substantially identical to each other, except for positions of a backlight unit and an observer.
- Table 1 is a simulation result for a viewing angle characteristic at an inclination angle of 70° according to design values (in-plane retardation value and thickness retardation value) of a polarizer plate protective film and the positive biaxial retardation film under the first IPS-LCD structure shown in FIG. 4a .
- the simulation is carried out with conditions representing the superior viewing angle characteristic at all inclination angles in all azimuthal angles by taking the retardation values of internal protective films of the first and second polarizer plates 1 and 2, the in-plane retardation value and the thickness retardation value of the positive biaxial retardation film 11, and an Nz representing biaxiality into consideration.
- the Nz is an index representing biaxiality of the positive biaxial retardation film, which can be defined as follows by using the refractive indexes of the film in three axis directions.
- N z n x ⁇ n z n x ⁇ n y
- Table 1 shows the improvement in the viewing angle characteristic according to the design values of the polarizer plate protective film and the positive biaxial retardation film.
- the IPS-LCD which does not use the viewing angle compensation film has a minimum CR (contrast ratio) of about 7 : 1
- the IPS-LCD represents the CR above 30 : 1 at an inclination angle of 70°, it means that the CR value above 30 : 1 can be obtained in all viewing angles, resulting in a much improvement of the viewing angle characteristic.
- Table 2 shows a simulation result when practical design values of a retardation film are applied to the IPS-LCD structure shown in FIG. 4b .
- Table 2 Internal protective film of 1 st polarizer plate IPS-Panel Positive biaxial retardation film Internal protective film of 2 nd polarizer plate Minimum contrast ratio at inclination angle of 70° R in (nm) R th (nm) Nz 40um TAC 250 170 76 0.55 40um TAC 83 290 160 88 0.45 83 330 155 102 0.34 83
- Table 2 shows the improvement in the viewing angle characteristic according to the design values of the polarizer plate protective film and the positive biaxial retardation film. If 40um TAC (triacetate cellulose) is used as a polarizer plate protective film, the polarizer plate protective film has a negative R th lower than an R th of the polarizer plate protective film of 80um TAC, so the design value of the positive biaxial retardation film is changed. Accordingly, it is possible to obtain a superior viewing angle characteristic by varying the design values. In detail, it is possible to obtain the CR more than 80 : 1 at an inclination angle of 70° by adjusting the design values of the polarizer plate protective film and the positive biaxial retardation film.
- 40um TAC triacetate cellulose
- an in-plane switching liquid crystal display including a first positive biaxial retardation film 11 aligned between an IPS panel 3 and a first polarizer plate 1, and a second positive biaxial retardation film 13 aligned between the IPS panel 3 and a second polarizer plate 2, in which an optical axis 12 of the first positive biaxial retardation film 11 is parallel to an absorption axis 4 of the first polarizer plate 1 and an optical axis 14 of the second positive biaxial retardation film 13 is perpendicular to an absorption axis 5 of the second polarizer plate 2, with the first positive biaxial retardation film 11 having an in-plane retardation value equal to or less than 190nm at a wavelength of 550nm and the second positive biaxial retardation film 13 having an in-plane retardation value in a range of 150 to 350nm at a wavelength of 550nm.
- the viewing angle characteristic of the IPS-LCD may be lowered due to a geometrical problem of the polarizer plate depending on the viewing angle and a dependency of the retardation value of the IPS-LCD panel to the viewing angle.
- the black state of the LCD is obtained by using two polarizer plates, in which a light generated from the backlight unit and linearly polarized by the first polarizer plate is absorbed by means of the absorption axis of the second polarizer plate.
- a slantingly incident light creates a rotated linearly polarized light which has been rotated after passing through the polarizer plate, and experiences the absorption axis of the second polarizer plate rotated.
- the linearly polarized light introduced through the first polarizer plate is not perpendicular to the absorption axis of the second polarizer plate, so a light component, which is parallel to a transmission axis, is created.
- the linearly polarized light greatly deviates from the perpendicular state with respect to the transmission axis, so light components in parallel to the transmission axis may increase. For this reason, the light leakage may occur in the black state.
- the light leakage under the black state of the LCD is a main factor causing deterioration of the viewing angle characteristic of the LCD.
- the light leakage increases according to an increase of the inclination angle and the increase of the light leakage lowers the CR and increases a color shift.
- the light which has been linearly polarized after passing through the first polarizer plate must match with the absorption axis of the second polarizer plate.
- the present invention utilizes the positive biaxial retardation film. In order to allow the light, which has been linearly polarized, to match with the absorption axis of the second polarizer plate according to the inclination angle, the in-plane retardation value and the thickness retardation value are necessary.
- the absorption axis of the first polarizer plate must match with the optical axis of the first positive biaxial retardation film, so as that a predetermined elliptically polarized light can be created through the first positive biaxial retardation film. Then, the elliptically polarized light turns into a linearly polarized light matching with the absorption axis of the polarizer plate through the second positive biaxial retardation film. To this end, the optical axis of the second positive biaxial retardation film must be aligned perpendicularly to the absorption axis of the second positive biaxial retardation film.
- the first positive biaxial retardation film having an in-plane retardation value equal to or less than 190nm
- the first positive biaxial retardation film converts the light, which has been linearly polarized through the first polarizer plate, into an elliptically polarized light, which is required for generating the linearly polarized light which matches with the absorption axis of the second polarizer plate after the light has passed through the second positive biaxial retardation film.
- the second positive biaxial retardation film converts the elliptically polarized light formed through the first positive biaxial retardation film into the linearly polarized light.
- the second positive biaxial retardation film having the retardation value in a range of about 150nm to 350nm is used according to the polarizing state of the light created by the first positive biaxial retardation film, it is possible to obtain the linearly polarized light which matches with the absorption axis of the second polarizer plate.
- FIGS. 5a and 5b The non-inventive second embodiment of the present invention is illustrated in FIGS. 5a and 5b , and the structures of the IPS-LCDs shown in FIGS. 5a and 5b are substantially identical to each other, except for positions of a backlight unit and an observer.
- Table 3 shows a simulation result when practical design values of a retardation film are applied to the second IPS-LCD structure shown in FIG. 5a or 5b .
- Table 3 (non-inventive examples) Internal protective film of 1 st polarizer plate Positive biaxial retardation film IPS-Panel Positive biaxial retardation film Internal protective film of 2 nd polarizer plate Minimum contrast ratio at angle of 70° Rin(nm) Rth(nm) Nz Rin(nm) Rth(nm) Nz COP 25 12.5 0.5 290nm 285 142 0.5 COP 238 35 17 0.5 230 115 0.5 40um TAC 160 60 30 0.5 200 100 0.5 80um TAC 55 40um TAC 160 88 0.45 302 151 0.5 COP 214 124 102 0.18 250 125 0.5 40um TAC 136 118 139 -0.17 220 110 0.5 80um TAC 50 80um TAC 160 49 0.72 350 175 0.5 COP 100 155 78 0.5 300
- the above simulation is carried out with conditions representing the superior viewing angle characteristic at all inclination angles in all azimuthal angles by taking the retardation values of internal protective films of the first and second polarizer plates 1 and 2, the in-plane retardation value and the thickness retardation value of the first and second positive biaxial retardation films 11 and 13, and an Nz representing biaxiality into consideration.
- Table 3 shows the minimum CR values at the inclination angle of 70° according to the design values (in-plane retardation value, thickness retardation value and internal protective film) of the first and second positive biaxial retardation films in the IPS-LCD.
- the most superior viewing angle characteristic is represented when a non oriented COP (cyclo olefin polymer) film having a thickness retardation value of 0 is used for the polarizer plate internal protective film.
- the polarizer plate may use internal and external protective films having unique negative thickness retardation values or internal and external protective films, which do not have the thickness retardation values.
- internal protective film includes non oriented COP (cyclo olefin polymer), 40um TAC(triacetate cellulose), 80um TAC(triacetate cellulose) or PNB (polynobonene).
- the thickness retardation value of the polarizer plate internal protective film is a very important factor when designing the retardation film such that the IPS-LCD represents low transmittance under a dark state at all inclination in all azimuthal angles.
- the internal protective film of the first polarizer plate 1 preferably has a thickness retardation value of 0 or a negative thickness retardation value. This is because the positive biaxial retardation film adjacent to the first polarizer plate 1 may compensate for the retardation value generated from the inner protective film of the first polarizer plate 1.
- the positive biaxial retardation film can be used as an inner protective film of at least one polarizer plate.
- the positive biaxial retardation films 11 and 13 are made from polymer materials or UV curable liquid crystal films.
- a center of a circle corresponds to an inclination angle of 0, and the inclination angle increases as a radius of the circle becomes enlarged.
- Numerals 20, 40, 60 and 80 marked along the radius of the circle in FIG. 6 represent the inclination angles.
- FIG. 6 shows the contrast characteristic in all viewing directions (inclination angles of 0° to 80° and azimuthal angles of 0° to 360°) when an upper polarizer plate is aligned in a direction of an azimuthal angle of 0°, and a lower polarizer plate is aligned in a direction of an azimuthal angle of 90°.
- An IPS-LCD which exclusively uses two polarizer plates, represents a contrast ratio equal to or less than 10:1 at an inclination angle of 70°.
- the IPS-LCD of the present invention represents a contrast ratio above 166:1 at an inclination angle of 70° as shown in FIG. 6 and Table 1.
- Internal protective films of polarizer plates 1 and 2 are made from COP.
- the in-plane switching liquid crystal display according to the present invention uses the positive biaxial retardation film while adjusting the optical axis direction and the retardation value of the positive biaxial retardation film, so the in-plane switching liquid crystal display can improve the contrast characteristic at a predetermined angular position as well as at a front position thereof, so that a color shift according to the viewing angle in the black state can be minimized.
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Description
- The present invention relates to a liquid crystal display (LCD), and more particularly to an in-plane switching liquid crystal display (IPS-LCD) including a compensation film, which uses a positive biaxial retardation film while adjusting an optical axis direction and a retardation value of the positive biaxial retardation film in order to improve a viewing angle characteristic of the in-plane switching liquid crystal display having a liquid crystal cell filled with liquid crystal of positive dielectric anisotropy (Δε>0) or negative dielectric anisotropy (Δε<0).
- Electrodes of an IPS-LCD are aligned in such a manner that an electric field is applied in parallel to a liquid crystal plane of the IPS-LCD. Surfaces of a liquid crystal layer adjacent to two substrates have pretilt angles in a range of 0° to 5° as disclosed in
U.S. Patent No. 6,078,375 . An IPS panel (liquid crystal cell) has an active matrix drive electrode comprising a pair of electrodes aligned in the same plane. In addition, the active matrix drive electrode provides IPS (In-Plain Switching), S-IPS (Super-In-Plain Switching) and FFS (Fringe Field Switching) modes to a liquid crystal layer formed between two glass substrates. According to the S-IPS mode, a two-domain liquid crystal alignment can be obtained by forming a zig-zag type electrode pattern, so an IPS color shift in a white state(Bright State) may be minimized. - The IPS-LCD is disclosed in
U.S. Patent No. 3,807,831 . However, the IPS-LCD disclosed inU.S. Patent No. 3,807,831 does not use a compensation film. Accordingly, the IPS-LCD represents a low contrast ratio at a predetermined inclination angle due to a relatively great amount of light leakage. -
U.S. Patent No. 5,189,538 discloses an LCD including two kinds of retardation films, such as a +A-plate and a positive biaxial retardation film, but it does not disclose information or technologies about the IPS-LCD. -
U.S. Patent No. 5,440,413 discloses a TN-LCD having two positive biaxial retardation films in order to improve the contrast characteristic and color characteristic of the TN-LCD at a predetermined inclination angle. - An IPS-LCD compensation film using one positive biaxial retardation film is disclosed in
U.S. Patent No. 6,285,430 . Characteristics of the IPS-LCD are as follows: - One positive biaxial retardation film is aligned between a polarizer plate and a liquid crystal layer.
- An in-plane retardation value of the biaxial retardation film is about 190nm to 390nm.
- An in-plane retardation value of the biaxial retardation film increases in proportional to an absolute value of a retardation in a direction of thickness of a polarizer plate protection film.
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KR 2003 0079705 A - A main object of using the biaxial retardation film is to improve a contrast characteristic of the IPS-LCD at an inclination angle in all azimuthal angles, especially 45°, 135°, 225° and 315°. Although the contrast characteristic of the IPS-LCD can be improved at the above azimuthal angles, the IPS-LCD in a black state represents a great amount of light leakage at other azimuthal angles. For this reason, a contrast ratio of the IPS-LCD is relatively reduced at other azimuthal angles. Therefore, the above IPS-LCD has a disadvantage in that the IPS-LCD represents a relatively low contrast ratio at specific azimuthal angles due to relatively great light leakage in the black state.
-
-
FIG. 1 is a view illustrating a basic structure of an IPS-LCD. -
FIG. 2 is a view illustrating an alignment of an absorption axis of a polarizer plate and an optical axis of liquid crystal in IPS-LCD panel ofFig. 1 . -
FIG. 3 is a view illustrating a refractive index of a retardation film. -
FIGS. 4a and 4b are views illustrating a structure of a first IPS-LCD including a viewing angle compensation film according to one embodiment of the present invention. -
FIGS. 5a and 5b are views illustrating a structure of a second IPS-LCD including a viewing angle compensation film according to one embodiment of the present invention. -
FIGS. 6 and 7 are graphs representing simulation results for a contrast characteristic at inclination angles of about 0° to 80° in all azimuthal angles when a white light is used in an IPS-LCD structure including a viewing angle compensation film according to one embodiment of the present invention, in whichFIG. 6 is a simulation result of a first IPS-LCD structure, andFIG. 7 is a simulation result of a second IPS-LCD structure. - It is an object of the present invention to provide an IPS-LCD capable of obtaining a high contrast characteristic at all inclination angles in all azimuthal angles as well as at a front position.
- Another object of the present invention is to provide an IPS-LCD representing low transmittance in a black state at all inclination angles in all azimuthal angles.
- The present invention accomplishes the above object by using a positive biaxial retardation film while adjusting an optical axis direction and the retardation value of the positive biaxial retardation film.
- In order to accomplish the above object, there is provided an in-plane switching liquid crystal display comprising: a first polarizer plate; a second polarizer plate; and a liquid crystal cell, which is horizontally aligned between two glass substrates and filled with liquid crystal of positive dielectric anisotropy (Δε>0) or negative dielectric anisotropy (Δε<0), an optical axis of the liquid crystal filled in the liquid crystal cell being aligned in-plane in parallel to the first and second polarizer plates, wherein an absorption axis of the first polarizer plate is perpendicular to an absorption axis of the second polarizer plate, the optical axis of the liquid crystal filled in the liquid crystal cell is parallel to the absorption axis of the first polarizer plate, a positive biaxial retardation film is aligned between the liquid crystal cell and the polarizer plate in order to compensate for a viewing angle, and an optical axis direction and a retardation value of the positive biaxial retardation film are adjusted according to an alignment order of positive biaxial retardation films, in accordance with
claim 1. - In order to compensate for the viewing angle of the in-plane switching liquid crystal display (IPS-LCD) in a black state, the present invention is characterized by using at least one positive biaxial retardation film in which an optical axis direction and a retardation value of the positive biaxial retardation film are adjusted according to upper and lower polarizer plates and an alignment order of the positive biaxial retardation films.
- A contrast ratio is an index representing a degree of definition for an image, and a high contrast ratio allows a high definition image. The contrast characteristic of the IPS-LCD is most deteriorated at an inclination angle of 70°. Thus, if the IPS-LCD represents an improved contrast characteristic at the inclination angle of 70°, it means that the contrast characteristic of the IPS-LCD is improved at all viewing angles. Accordingly, comparison of improvement for viewing angle characteristics of IPS-LCDs is preferably carried out with the inclination angle of 70°. When the IPS-LCD uses the only polarizer plates, a minimum contrast ratio at the inclination angle of 70° is equal to or less than 10:1. However, the IPS-LCD of the present invention uses the positive biaxial retardation film while adjusting the optical axis and the retardation value thereof, so the IPS-LCD of the present invention may represent a minimum contrast ratio above 20:1. Preferably, the IPS-LCD of the present invention represents the minimum contrast ratio above 20:1 at the inclination angle of 70°.
- Reference will now be made in detail to the present invention.
-
FIG. 1 is a view illustrating a basic structure of an IPS-LCD. - The IPS-LCD includes a
first polarizer plate 1, asecond polarizer plate 2 and aliquid crystal cell 3. Anabsorption axis 4 of thefirst polarizer plate 1 is aligned in perpendicular to the anabsorption axis 5 of thesecond polarizer plate 2 and theabsorption axis 4 of thefirst polarizer plate 1 is parallel to anoptical axis 6 of theliquid crystal cell 3. InFIG. 2 , twoabsorption axes optical axis 6 of one liquid crystal cell are shown. - The liquid crystal display using a compensation film according to the present invention includes the
first polarizer plate 1, theliquid crystal cell 3, which is horizontally aligned between two glass substrates and filled with liquid crystal of positive dielectric anisotropy (Δε>0) or negative dielectric anisotropy (Δε<0), and thesecond polarizer plate 2. Theoptical axis 6 of the liquid crystal filled in theliquid crystal cell 3 is aligned in-plane in parallel to the polarizer plates. Theabsorption axis 4 of thefirst polarizer plate 1 is aligned in perpendicular to theabsorption axis 5 of thesecond polarizer plate 2 and theabsorption axis 4 of thefirst polarizer plate 1 is parallel to theoptical axis 6 of the liquid crystal filled in theliquid crystal cell 3. In addition, one of the first and second substrates includes an active matrix drive electrode having a pair of electrodes, which is formed on a surface of the substrate adjacent to a liquid crystal layer. - A retardation value of the liquid crystal layer is defined as RLC = (nx,LC-ny,LC) x d, wherein d is a thickness of the liquid crystal layer. Preferably, the liquid crystal layer of the IPS panel according to the present invention has a retardation value in a range of 200nm to 400nm at a wavelength of 550nm.
- In order to make a white state when voltage is applied to the IPS-LCD panel, the light linearly polarized at 90° after passing through the first polarizer plate must be linearly polarized into 0° after it has passed through the liquid crystal layer. Further, in order to achieve the state of light polarized as described above, the retardation value of the liquid crystal layer of the IPS-LCD must be a half wavelength of 589nm (a monochromatic light representing a highest brightness which a person can feel). Therefore, in order to allow the light to produce a white color, the retardation value of the liquid crystal layer of the IPS-LCD can be adjusted to be somewhat shorter or longer than the half wavelength of 589nm. Therefore, the retardation value is preferably in the range around 295nm corresponding to the half wavelength of 589nm.
- The LCD of the present invention may align the liquid crystal in multi-directions, or the liquid crystal may be divided into multi-regions by voltage applied thereto.
- The LCDs can be classified into IPS (In-Plain Switching) LCDs, Super-IPS (Super-In-Plain Switching) LCDs and FFS (Fringe Field Switching) LCDs according to modes of the active matrix drive electrode including a pair of electrodes. In the present invention, the IPS-LCD may include the Super-IPS LCD, the FFS LCD, and a reverse TN IPS LCD.
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FIG. 3 illustrates a refractive index of a retardation film used for compensating for a viewing angle of the IPS-LCD. Referring toFIG. 3 , a refractive index in an x-axis direction is nx(8), a refractive index in a y-axis direction is ny (9), and a refractive index in a z-axis direction is nz (10). The characteristic of the retardation film depends on the refractive index. -
-
-
- The positive biaxial retardation
film satisfying Equation 3 represents mutually different refractive indexes in x-axis, y-axis and z-axis directions, so it has an in-plane retardation value and a thickness retardation value. The in-plane retardation value can be defined as follows by using in-plane refractive indexes of nx (8) and ny (9). -
- The positive biaxial retardation film signifies a film having the positive in-plane retardation value and the positive thickness retardation value.
- The wavelength dispersion characteristic of the positive biaxial retardation film includes normal wavelength dispersion, flat wavelength dispersion, and reverse wavelength dispersion. The unlimited example of the positive biaxial retardation film includes an UV curable liquid crystal film using a nematic liquid crystal and a biaxially oriented PC (polycarbonate).
- According to the present invention, the direction of the optical axis of the retardation film is determined according to an alignment order of the retardation film.
- According to a first embodiment of the present invention, there is provided an in-plane switching liquid crystal display including a positive
biaxial retardation film 11 aligned between anIPS panel 3 and asecond polarizer plate 2, in which anoptical axis 12 of the positivebiaxial retardation film 11 is perpendicular to anabsorption axis 5 of thesecond polarizer plate 2, with an in-plane retardation value of the positivebiaxial retardation film 11 equal to or less than 190nm at a wavelength of 550nm. - The optical axis of the retardation film relates to light leakage generated from two polarizer plates with the absorption axes thereof aligned perpendicularly to each other. That is, in order to minimize the light leakage of the polarizer plates, the in-plane optical axis of the positive biaxial retardation film must be aligned perpendicularly to the absorption axis of the polarizer plate adjacent to the positive biaxial retardation film.
- When the absorption axes of the polarizer plates are aligned in an angular direction of 0° and 90° respectively, if an observer checks the black state while inclining the polarizer plates in a direction of an azimuthal angle of 45°, it can be found that the light leakage increases as the inclination angle increases. This is because the angle between absorption axes of two polarizer plates greatly deviates from a perpendicular state as the inclination angle increases. That is, in order to minimize the light leakage, the polarized light must be rotated by an extent of angle as deviated from a perpendicular state. The light radiated from a backlight unit is linearly polarized after passing through the first polarizer plate, and a rotational angle of the linearly polarized light must be increased according to the inclination angle. In order to rotate the linearly polarized light, the in-plane optical axis of the positive biaxial retardation film must be aligned in perpendicular to the absorption axis of the adjacent polarizer plate.
- Meanwhile, in order to allow the linearly polarized light to rotate in match with the absorption axis of the second polarizer plate corresponding to an increase of the inclination angle, the in-plane retardation value of the positive biaxial retardation film is preferably set equal to or less than 190nm. At this time, the in-plane retardation value of the positive biaxial retardation film may vary according to the thickness retardation value of the positive biaxial retardation film. In order to properly compensate for the viewing angle, it is preferred to reduce the in-plane retardation value as the total thickness retardation value of the retardation film increases.
- The first embodiment of the present invention is illustrated in
FIGS. 4a and 4b , and the structures of the IPS-LCDs shown inFIGS. 4a and 4b are substantially identical to each other, except for positions of a backlight unit and an observer. - Table 1 is a simulation result for a viewing angle characteristic at an inclination angle of 70° according to design values (in-plane retardation value and thickness retardation value) of a polarizer plate protective film and the positive biaxial retardation film under the first IPS-LCD structure shown in
FIG. 4a .Table 1 Internal protective film of 1st polarizer plate IPS-Panel Positive biaxial retardation film Internal protective film of 2nd polarizer plate Minimum contrast ratio at inclination angle of 70° Rin(nm) Rth(nm) Nz COP 290nm 180 144 0.2 80um TAC 166 160 173 -0.08 120um TAC 83 40um TAC 160 88 0.45 40um TAC 83 124 102 0.18 80um TAC 79 118 139 -0.17 120um TAC 65 80um TAC 160 49 0.72 COP 33 155 78 0.5 40um TAC 30 110 77 0.3 80um TAC 30 - The simulation is carried out with conditions representing the superior viewing angle characteristic at all inclination angles in all azimuthal angles by taking the retardation values of internal protective films of the first and
second polarizer plates biaxial retardation film 11, and an Nz representing biaxiality into consideration. -
- Table 1 shows the improvement in the viewing angle characteristic according to the design values of the polarizer plate protective film and the positive biaxial retardation film. Referring to Table 1, since the IPS-LCD which does not use the viewing angle compensation film has a minimum CR (contrast ratio) of about 7 : 1, if the IPS-LCD represents the CR above 30 : 1 at an inclination angle of 70°, it means that the CR value above 30 : 1 can be obtained in all viewing angles, resulting in a much improvement of the viewing angle characteristic.
- In addition, Table 2 shows a simulation result when practical design values of a retardation film are applied to the IPS-LCD structure shown in
FIG. 4b .Table 2 Internal protective film of 1st polarizer plate IPS-Panel Positive biaxial retardation film Internal protective film of 2nd polarizer plate Minimum contrast ratio at inclination angle of 70° Rin(nm) Rth(nm) Nz 40um TAC 250 170 76 0.55 40um TAC 83 290 160 88 0.45 83 330 155 102 0.34 83 - Table 2 shows the improvement in the viewing angle characteristic according to the design values of the polarizer plate protective film and the positive biaxial retardation film. If 40um TAC (triacetate cellulose) is used as a polarizer plate protective film, the polarizer plate protective film has a negative Rth lower than an Rth of the polarizer plate protective film of 80um TAC, so the design value of the positive biaxial retardation film is changed. Accordingly, it is possible to obtain a superior viewing angle characteristic by varying the design values. In detail, it is possible to obtain the CR more than 80 : 1 at an inclination angle of 70° by adjusting the design values of the polarizer plate protective film and the positive biaxial retardation film.
- According to a non-inventive second embodiment of the present invention, there is provided an in-plane switching liquid crystal display including a first positive
biaxial retardation film 11 aligned between anIPS panel 3 and afirst polarizer plate 1, and a second positivebiaxial retardation film 13 aligned between theIPS panel 3 and asecond polarizer plate 2, in which anoptical axis 12 of the first positivebiaxial retardation film 11 is parallel to anabsorption axis 4 of thefirst polarizer plate 1 and anoptical axis 14 of the second positivebiaxial retardation film 13 is perpendicular to anabsorption axis 5 of thesecond polarizer plate 2, with the first positivebiaxial retardation film 11 having an in-plane retardation value equal to or less than 190nm at a wavelength of 550nm and the second positivebiaxial retardation film 13 having an in-plane retardation value in a range of 150 to 350nm at a wavelength of 550nm. - The viewing angle characteristic of the IPS-LCD may be lowered due to a geometrical problem of the polarizer plate depending on the viewing angle and a dependency of the retardation value of the IPS-LCD panel to the viewing angle. The black state of the LCD is obtained by using two polarizer plates, in which a light generated from the backlight unit and linearly polarized by the first polarizer plate is absorbed by means of the absorption axis of the second polarizer plate. However, unlike a vertical incident light, a slantingly incident light creates a rotated linearly polarized light which has been rotated after passing through the polarizer plate, and experiences the absorption axis of the second polarizer plate rotated. Therefore, the linearly polarized light introduced through the first polarizer plate is not perpendicular to the absorption axis of the second polarizer plate, so a light component, which is parallel to a transmission axis, is created. As the inclination angle becomes enlarged, the linearly polarized light greatly deviates from the perpendicular state with respect to the transmission axis, so light components in parallel to the transmission axis may increase. For this reason, the light leakage may occur in the black state.
- The light leakage under the black state of the LCD is a main factor causing deterioration of the viewing angle characteristic of the LCD. The light leakage increases according to an increase of the inclination angle and the increase of the light leakage lowers the CR and increases a color shift. Thus, it is possible to improve the viewing angle characteristic by minimizing the light leakage under the black state depending on the inclination angle. In order to improve the viewing angle characteristic, the light which has been linearly polarized after passing through the first polarizer plate must match with the absorption axis of the second polarizer plate. To this end, the present invention utilizes the positive biaxial retardation film. In order to allow the light, which has been linearly polarized, to match with the absorption axis of the second polarizer plate according to the inclination angle, the in-plane retardation value and the thickness retardation value are necessary.
- The absorption axis of the first polarizer plate must match with the optical axis of the first positive biaxial retardation film, so as that a predetermined elliptically polarized light can be created through the first positive biaxial retardation film. Then, the elliptically polarized light turns into a linearly polarized light matching with the absorption axis of the polarizer plate through the second positive biaxial retardation film. To this end, the optical axis of the second positive biaxial retardation film must be aligned perpendicularly to the absorption axis of the second positive biaxial retardation film. If the first positive biaxial retardation film having an in-plane retardation value equal to or less than 190nm is employed, the first positive biaxial retardation film converts the light, which has been linearly polarized through the first polarizer plate, into an elliptically polarized light, which is required for generating the linearly polarized light which matches with the absorption axis of the second polarizer plate after the light has passed through the second positive biaxial retardation film.
- The second positive biaxial retardation film converts the elliptically polarized light formed through the first positive biaxial retardation film into the linearly polarized light. In addition, if the second positive biaxial retardation film having the retardation value in a range of about 150nm to 350nm is used according to the polarizing state of the light created by the first positive biaxial retardation film, it is possible to obtain the linearly polarized light which matches with the absorption axis of the second polarizer plate.
- The non-inventive second embodiment of the present invention is illustrated in
FIGS. 5a and 5b , and the structures of the IPS-LCDs shown inFIGS. 5a and 5b are substantially identical to each other, except for positions of a backlight unit and an observer. - Table 3 shows a simulation result when practical design values of a retardation film are applied to the second IPS-LCD structure shown in
FIG. 5a or 5b .Table 3 (non-inventive examples) Internal protective film of 1st polarizer plate Positive biaxial retardation film IPS-Panel Positive biaxial retardation film Internal protective film of 2nd polarizer plate Minimum contrast ratio at angle of 70° Rin(nm) Rth(nm) Nz Rin(nm) Rth(nm) Nz COP 25 12.5 0.5 290nm 285 142 0.5 COP 238 35 17 0.5 230 115 0.5 40um TAC 160 60 30 0.5 200 100 0.5 80um TAC 55 40um TAC 160 88 0.45 302 151 0.5 COP 214 124 102 0.18 250 125 0.5 40um TAC 136 118 139 -0.17 220 110 0.5 80um TAC 50 80um TAC 160 49 0.72 350 175 0.5 COP 100 155 78 0.5 300 150 0.5 40um TAC 68 - The above simulation is carried out with conditions representing the superior viewing angle characteristic at all inclination angles in all azimuthal angles by taking the retardation values of internal protective films of the first and
second polarizer plates biaxial retardation films - Table 3 shows the minimum CR values at the inclination angle of 70° according to the design values (in-plane retardation value, thickness retardation value and internal protective film) of the first and second positive biaxial retardation films in the IPS-LCD. The most superior viewing angle characteristic is represented when a non oriented COP (cyclo olefin polymer) film having a thickness retardation value of 0 is used for the polarizer plate internal protective film.
- The polarizer plate may use internal and external protective films having unique negative thickness retardation values or internal and external protective films, which do not have the thickness retardation values.
- The unlimited example of internal protective film includes non oriented COP (cyclo olefin polymer), 40um TAC(triacetate cellulose), 80um TAC(triacetate cellulose) or PNB (polynobonene).
- The thickness retardation value of the polarizer plate internal protective film is a very important factor when designing the retardation film such that the IPS-LCD represents low transmittance under a dark state at all inclination in all azimuthal angles.
- The internal protective film of the
first polarizer plate 1 preferably has a thickness retardation value of 0 or a negative thickness retardation value. This is because the positive biaxial retardation film adjacent to thefirst polarizer plate 1 may compensate for the retardation value generated from the inner protective film of thefirst polarizer plate 1. - In addition, the positive biaxial retardation film can be used as an inner protective film of at least one polarizer plate.
- Preferably, the positive
biaxial retardation films -
- Hereinafter, preferred embodiments of the present invention will be described. However, it is noted that the preferred embodiments described below are used for illustrative purpose and the present invention is not limited thereto.
- The IPS-LCD shown in
FIG. 4a includes an IPS liquid crystal cell filled with liquid crystal having a cell gap of 2.9 µm, a pretilt angle of 3°, dielectric anisotropy of Δε = +7, and a birefringence of Δn = 0.1. An UV curable liquid crystal film having an in-plane retardation value Rin = 180nm and a thickness retardation value Rth = 144nm at a wavelength of 550nm is used for a positivebiaxial retardation film 11. A COP internal protective film having a retardation value of almost 0 is used as an internal protective film of afirst polarizer plate 1 and 80µm TAC having a thickness retardation value of Rth = -64nm at a wavelength of 550nm is used as an internal protective film of asecond polarizer plate 2. When a white light is used, the simulation result for the contrast characteristic of a first IPS-LCD structure including a viewing angle compensation film at an inclination angle of about 0° to 80° in all azimuthal angles is illustrated inFIG. 6 and Table 1. - Referring to
FIG. 6 , a center of a circle corresponds to an inclination angle of 0, and the inclination angle increases as a radius of the circle becomes enlarged.Numerals FIG. 6 represent the inclination angles. - In addition, numerals 0 to 360 marked along a circumference of the circle represent the azimuthal angles.
FIG. 6 shows the contrast characteristic in all viewing directions (inclination angles of 0° to 80° and azimuthal angles of 0° to 360°) when an upper polarizer plate is aligned in a direction of an azimuthal angle of 0°, and a lower polarizer plate is aligned in a direction of an azimuthal angle of 90°. An IPS-LCD, which exclusively uses two polarizer plates, represents a contrast ratio equal to or less than 10:1 at an inclination angle of 70°. However, the IPS-LCD of the present invention represents a contrast ratio above 166:1 at an inclination angle of 70° as shown inFIG. 6 and Table 1. - The IPS-LCD shown in
FIG. 5b includes an IPS liquid crystal cell filled with liquid crystal having a cell gap of 2.9µm, a pretilt angle of 3°, dielectric anisotropy of Δε = +7, and a birefringence of Δn = 0.1. An UV curable liquid crystal film having an in-plane retardation value Rin = 20nm and a thickness retardation value Rth = 10nm at a wavelength of 550nm is used for a first positivebiaxial retardation film 11. In addition, an UV curable liquid crystal film having an in-plane retardation value Rin = 288nm and a thickness retardation value Rth = 144nm at a wavelength of 550nm is used for a second positivebiaxial retardation film 13. Internal protective films ofpolarizer plates FIG. 7 . - As can be seen from the foregoing, the in-plane switching liquid crystal display according to the present invention uses the positive biaxial retardation film while adjusting the optical axis direction and the retardation value of the positive biaxial retardation film, so the in-plane switching liquid crystal display can improve the contrast characteristic at a predetermined angular position as well as at a front position thereof, so that a color shift according to the viewing angle in the black state can be minimized.
- While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment and the drawings, but, on the contrary, it is intended to cover various modifications and variations within the scope of the appended claims.
Claims (4)
- An in-plane switching liquid crystal display comprising:a first polarizer plate (1);a second polarizer plate (2); anda liquid crystal cell (3), which is horizontally aligned and filled with liquid crystal of positive dielectric anisotropy (Δ ε>0) or negative dielectric anisotropy (Δε<0), an optical axis (6) of the liquid crystal filled in the liquid crystal cell (3) being aligned in-plane in parallel to the first and second polarizer plates (1, 2),wherein an absorption axis (4) of the first polarizer plate (1) is perpendicular to an absorption axis (5) of the second polarizer plate (2), the optical axis (6) of the liquid crystal filled in the liquid crystal cell (3) is parallel to the absorption axis (4) of the first polarizer plate (1), a positive biaxial retardation film (11; 13) defined by a following Equation is aligned between the liquid crystal cell (3) and the second polarizer plate (2), an optical axis (12; 14) of the positive biaxial retardation film (11; 13) is perpendicular to the absorption axis (5) of the second polarizer plate (2)wherein nx and ny are in-plane refractive indexes, nz is a thickness refractive index, and the positive biaxial retardation film (11; 13) has a positive in-plane retardation value (Rin = d × (nx - ny)) and a positive thickness retardation value (Rth = d × (nz - ny)) in which d is a thickness of a film,characterized in that an in-plane retardation value of the positive biaxial retardation film (11; 13) is equal to or less than 180nm at a wavelength of 550nm and that the positive biaxial retardation film (11; 13) has a normal wavelength dispersion or flat wavelength dispersion characteristic, and that the first polarizer plate (1) and the second polarizer plate (2) have internal protective films respectively.
- The in-plane switching liquid crystal display as claimed in claim 1, wherein the internal protective film of the second polarizer plate (2) has a negative thickness retardation value.
- The in-plane switching liquid crystal display as claimed in claim 1, wherein a retardation value of the liquid crystal cell (3) is in range of 200nm to 400nm at a wavelength of 550nm.
- The in-plane switching liquid crystal display as claimed in claim 1, wherein the internal protective film of the first polarizer plate (1) has a thickness retardation value of 0 or a negative thickness retardation value.
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KR1020030083023A KR100601916B1 (en) | 2003-11-21 | 2003-11-21 | In-plane switching liquid crystal display comprising compensation film for angular field of view using positive biaxial retardation film |
EP04819017.7A EP1685441B1 (en) | 2003-11-21 | 2004-11-17 | In-plane switching liquid crystal dislpay comprising compensation film for angular field of view using positive biaxial retardation film |
PCT/KR2004/002971 WO2005050302A1 (en) | 2003-11-21 | 2004-11-17 | In-plane switching liquid crystal dislpay comprising compensation film for angular field of view using positive biaxial retardation film |
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EP04819017.7A Division-Into EP1685441B1 (en) | 2003-11-21 | 2004-11-17 | In-plane switching liquid crystal dislpay comprising compensation film for angular field of view using positive biaxial retardation film |
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EP16195465.6A Active EP3153920B1 (en) | 2003-11-21 | 2004-11-17 | In-plane switching liquid crystal display comprising compensation film for angular field of view using positive biaxial retardation film |
EP04819017.7A Active EP1685441B1 (en) | 2003-11-21 | 2004-11-17 | In-plane switching liquid crystal dislpay comprising compensation film for angular field of view using positive biaxial retardation film |
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US20090115944A1 (en) | 2009-05-07 |
TW200525236A (en) | 2005-08-01 |
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WO2005050302A1 (en) | 2005-06-02 |
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JP4468899B2 (en) | 2010-05-26 |
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EP2762966B1 (en) | 2017-01-04 |
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